Studies are proposed on the role of early social experience and hormonal influences in the ontogeny and social expression of fearful and evasive behaviors. A laboratory paradigm has been developed for eliciting alarm signals in domestic chickens under controlled conditions using moving predator models as stimuli. Previous research has demonstrated that adult males do not emit alarm signals in response to a given predator stimulus in a reflexive fashion, but rather modulate their alarm calling behavior in response to their social environment. That is, they behave as though they are responsive both to the predator and to the presence of a potential signal receiver. In chickens, as in many other birds, social behaviors, such as following movements of chicks and sexual behavior in adults, are known to be decisively influenced by events during sensitive periods in early development (imprinting). Experiments are proposed (1) to establish whether the social environment in which young birds are reared determine their later social pattern of alarm calling and other fearful and evasive behaviors, and (2) to investigate whether a sensitive period for that influence can be delimited. Pilot experiments suggest that in males there is a positive correlation between the frequency of alarm calling under seminatural field conditions and plasma testosterone levels. Moreover, castrated birds do not give alarm calls. Accordingly, further experiments are proposed (3) to study the normal time course of alarm call development and its relationship to circulating testosterone levels, (4) to document the effects on male calling of castration and testosterone replacement therapy, and (5) to develop a behavior assay using testosterone to induce premature alarm calling in young birds. Detailed examination of the acoustic morphology of vocal signals will be a key component of the analysis. Results will be interpreted in the light of the immediate social environment and past developmental social history of the birds. Blood samples will be drawn at frequent intervals in parallel with the testing of alarm calling and evasive behaviors and subjected to radioimmunoassay for testosterone levels.